The invention relates to a control mechanism for a vehicle transmission gearbox which can be shifted between a neutral position and non-neutral positions.
In gearboxes which are mechanically shifted by a shift lever between a neutral position and gear ratio position or between differing gear ratios, the correct position of the lever is not always reached. Instead, the lever may be placed in an intermediate position associated with neither the neutral position nor a specific gear ratio of the gearbox. It is desirable to provide a control mechanism which assures that the lever will not be left in an intermediate position, and that the lever will be in a desired particular position, even though no detent positions are provided on the gearshift lever.
The lever may be left in an intermediate position as a result of insufficient forces being applied to the lever. Or, this may be the result of excessively large tolerances in the linkages between shift lever and gearbox, or may be the result of wear. The requirements of tight tolerances and durability, however, increase the technical expense and the costs of the transmission elements. If push-pull control cables are applied between the shift lever and the gearbox, added difficulties are presented by play that varies with load, friction, corrosion, erroneous adjustments and tight routing radii of the control cable.
In EP-A-0 737 826 a gearshift lever is connected to a gearbox through a flexible cable. The gearshift lever can be pivoted about two axes that are perpendicular to each other. In order to retain the gearshift lever reliably with respect to a direction of pivoting in a desired central neutral position or in a deflected position in which a gear ratio is engaged, the direction of pivoting is controlled by a helical spring. The core of the helical spring is supported on a pin. The legs of the helical spring that extend outward engage an elongated hole in a pivoted lever that is fastened to the gearshift lever and force the latter into a central position which corresponds to the neutral position. The elongated hole contains detent positions that are intended to retain the gearshift lever in a gear ratio engagement position.